A flat panel display element performs a very important role of supporting an advanced image information society that has recently quickly grown mainly in the internet field. Especially, an organic electro-luminescence element (organic EL element) that can be driven at a low voltage in a self-emission manner is excellent in a viewing angle and a contrast ratio, compared to a liquid crystal display (LCD) (the most widely used flat panel display element). Also, the organic electro-luminescence element does not require a backlight, and thus can be manufactured in such a manner that it can have a light weight and a thin thickness. Also, it is advantageous in view of power consumption. Furthermore, it has been spotlighted as a next generation display device due to a high response speed, and a wide color reproduction range. In general, an organic electro-luminescence element has an anode including a transparent electrode, an organic material layer including a light emitting area, and a metal electrode (cathode), which are sequentially formed on a glass substrate.
Herein, the organic material layer may include not only an emitting layer (EML) but also a hole injection layer (HIL), a hole transport layer (HTL), an electron transport layer (ETL) or an electron injection layer (EIL). For light emission of an emitting layer, it may further include an electron blocking layer (EBL) or a hole blocking layer (HBL). When an organic electro-luminescence element with such a structure is applied with an electric field, holes are injected from the anode, and electrons are injected from the cathode. The injected holes and electrons are transferred from the hole transport layer and the electron transport layer, respectively, and recombined in the emitting layer so as to form light emitting excitons. The formed light emitting excitons are transited to ground states while emitting light. Herein, in order to increase the efficiency and stability of a light emission state, a light emitting pigment (guest) may be doped in the emitting layer (host).
In order to utilize such an organic electro-luminescence element in various display media, the life span of a device is most important. At present, much research on improvement of the life span of an organic electro-luminescence element has been conducted.